Over the years, a number of devices and techniques have been proposed to provide a greater degree of assurance that a sterilizer is operating effectively to exclude air which could prevent direct contact of steam with the objects being sterilized. In some cases, these have been adopted by hospitals convinced that they needed more reliability.
Efforts to mechanically assure the complete removal of air from steam sterilizers have not been fully successful. Prior to the publication of the Bowie and Dick test in 1963, co-developer J. Dick had employed thermocouples in a simpler form of the test, one in a test package and another at the sterilizer drain. With most loads like the towel package, however, it is not possible to predict the location of the air bubble with the certainty required. The published version of the test replaced the thermocouple with a heat-sensitive tape to better indicate the extent of air incorporation, but still required monitoring drain temperatures. In U.S. Pat. No. 3,967,494, Joslyn disclosed a method and apparatus for detecting entrapped air in a steam sterilizer. The device is shown outside the steam chamber to enable quantitative measurement of the amount of air or other noncondensible gas at the chamber drain. The device is intended for use with a sterilizer of the type that employs steam to displace air. The device does not, however, eliminate the need for a Bowie and Dick test.
In U.S. Pat. No. 4,372,916, Chamberlain and Cook monitor the temperature of the exhausted steam at the drain and the pressure within the chamber, and compare these to the steam table values to determine if all the air has been evacuated. The positioning of sensors within the chamber, especially by retrofitting, can, however, create further problem areas for future concern.
In U.S. Pat. No. 4,115,068, Joslyn describes a small device for indicating air inside a sterilization chamber of the type used with steam or ethylene oxide. The device includes an upright tube holding an indicator strip and a heat sink. Air is said to pass into the tube where it interferes with the steam contacting the indicator strip. Dyke and Oshlag comment on this arrangement in U.S. Pat. No. 4,594,223, indicating that steam, which is less dense than air, is required to work against the weight of any accumulated air. To correct this, they describe a device having a depending glass chamber which permits air to settle to the bottom along with water from condensed steam. This device, like that of Joslyn, is simply a replacement for the Bowie and Dick test and requires interpretation of the test results--a source of frequent errors in the original Bowie and Dick test. This is true also of a related device disclosed by Augurt in U.S. Pat. No. 5,066,464, which has a strip of heat-sensitive material in a horizontally-disposed chamber. Similarly, U.S. Pat. No. 4,486,387 to Augurt and U.S. Pat. No. 4,596,696 to Scoville, describe disposable test packages which have Bowie and Dick type test sheets which require interpretation.
There remains a need for a method and apparatus to more objectively, reliably, and precisely determine the effective operation of a steam sterilizer. There is especially a need for a test which provides a positive indication of problems or the absence of them and decreases the probability that either (1) the test performance or (2) interpretation of the results will be dependent upon the skills of a particular operator--both, areas of concern in Bowie and Dick testing.